Ofloxacin, 9-fluoro-3-methyl-10-(4-methyl-1-piperazinyl) -7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de)[1,43-benzoxazin-6-carboxylic acid, having the following formula is knowr as disclosed in Japanese Patent 1,444,043; U.S. Pat. No. 4,382,892; and EP-B-0,047,005, as an excellent synthetic antibacterial agent and has been marketed in many countries. The 3-(S)-isomer of Ofloxacin possesses excellent potency as synthetic antimicrobial agent as disclosed in EP-A-0,206,283. ##STR2##